Figure 1(a) shows the magnetization curves of anatase Ti\(_{1-x}\) Co\(_x\) O\(_{2-\delta }\)  (\(x\)  = 0.05) at 300 K for various carrier densities (\(n_e\) ). The \(n_e\)  for metallic, intermediate and insulating samples were 4.1 \(\times \)  \(10^{19}\) , 1.1 \(\times \)  \(10^{19}\)  and 4.0 \(\times \)  \(10^{18}\)  cm\(^{-3}\) , respectively. That of metallic rutile thin films which has the carrier density of 7 \(\times \)  \(10^{21}\)  cm\(^{-3}\)  is also shown in Fig 1(b). The saturation magnetization of the anatase sample is 0.6-2.1 \(\mu _B\) /Co with a coercive force of \(\sim \) 100 to 200 Oe. In the M(H) measurements, magnetic field was applied parallel to the the direction of anatase (001). Anomalous Hall-effect (AHE) measurements for anatase Ti\(_{1-x}\) Co\(_x\) O\(_{2-\delta }\)  with various \(n_e\)  also show similar magnetic field dependences [1]}. From Fig. 1, it is clear that the magnetization of the anatase thin films is larger than the rutile thin films, which may be attributed to the fact that anatase films in this study have a mobility \(\sim \) 2-11 cm\(^2\) V\(^{-1}\) s\(^{-1}\)  which is two orders of the magnitude higher than the mobility of rutile thin films [2]}.
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